The present silicon semiconductor element has remarkably improved the ability of computers by its hyperfine structure and integrated structure into high density. In the silicon semiconductor elements, an n-type or p-type semiconductor is made by doping a very small amount of impurities into silicon. However, by a progress of hyperfine processing, the number of impurity atoms contained in one element has been extremely decreased, and as a result, the element cannot work as a semiconductor any longer in principle. The dimension of the element considered to be the limit is a plurality of tens of nm, and if a hyperfine processing technology advances at a current pace, it is predicted that the limit will be reached after a plurality of tens of years.
In a fine processing technology by optical lithography using a chemical amplification type photo resist, the applied light has been shifted from visible light to ultraviolet light or deep ultraviolet light, but the limit of resolution is considered to be about 70 nm. Recently, an application of lithography using an X-ray, a focused ion beam and an electron beam, which have shorter radiation wavelengths has been investigated. However, in order to use these radiation wavelengths, the development of a new photo resist, an electron beam resist, an optical system and a mask, and the reduction of a manufacturing cost are necessary and expected. However, the technical and practical problems have not been improved yet at this stage. Accordingly, the technology based on a top-down concept reaches a limit.
As for a technology based on a bottom-up concept, a technique using a scanning probe microscope captures attention at present. One of the technologies can make a nanometric structure by disposing and reacting atoms or molecules in an arbitrary place with the use of a scanning tunneling microscope (STM). The study is described, for instance, in a scientific magazine, Nature, 409, 683 (2001) by Y. Okawa and M. Aono. Another technology has succeeded in the production of a self-organization film which is patterned in a nanometric order, by drawing the pattern on a substrate with a solution of thiol molecules coated on the top of a fine needle in an atomic force microscope (AFM). The study is described, for instance, in a scientific magazine, Science, 283, 661 (1999) by R. D. Piner, J. Zhu, F. Xu, S. Hong and C. A. Mirkin. Both technologies are excellent techniques for making a two-dimensional structure in a nanometric region, but are difficult to construct a three-dimensional structure, and are not practical from the viewpoint of a manufacturing cost.
The above-described methods for making a device are based on the concept of the so-called top-down technology, and have difficulty in producing a three-dimensional molecular device having a smaller size.
At present, a new molecular device of highly dense molecules, which can be operated even though having a dimension of a nanometric level, is energetically developed in a worldwide scale. For instance, a single electron element capable of controlling the switching on and off with one electron, and a molecular device using a functional organic molecule as a molecular structure are proposed. In order to put the molecular devices based on new concepts to practical use, many problems must be still solved. One big problem among them is how to selectively combine individual molecules. This is the big problem of the bottom-up technique, and is mentioned in Nikkei Science of a scientific magazine, 2001, December, page 37. However, an effective method for controlling the coupling of individual molecular elements has not been found until now.